In communication systems, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communication system is deployed.
Orthogonal Frequency Division Multiplexing (OFDM) modulation and Discrete Multi-Tone (DMT) modulation are state-of-the-art physical-layer modulation techniques used in a number of wireless and wireline communication systems.
Examples include, but are not limited to, the long term evolution (LTE) 4:th generation (4G) mobile communication standard and the high-speed access-technology standards A/VDSL (Very-high-bit-rate digital subscriber line) and G.fast. OFDM/DMT has a number of advantages. Some of these advantages include, but are not limited to, high spectral efficiency, low-complexity implementation of modulator and demodulator, low-complexity mitigation of large delay spreads (or equivalently, large frequency selectivity), and high flexibility. The most notable drawbacks are high peak-to-average-power ratio (PAPR) of the transmit signal and high in-band spectral leakage.
Flexibility in control over the transmit spectrum and good in-band as well as out-of-band suppression are advantageous for many communication systems. When attempting to feed wireless signals over band-limited, guided channels (such as coaxial cables, copper cables of various grades, power lines, etc.), spectrum control and out-of-band suppression are of importance. Good spectral suppression enables tight packing of multiple transmission signals (corresponding, for example, to different antenna streams or transmit directions) into the band offered by a guided channel.
A first group of existing spectral suppression methods typically enable a modest spectrum-shaping capability not yielding the desired out-of-band suppression. A second group of existing spectral suppression methods provides a higher spectrum-shaping capability than methods of the first group, but introduces pre-distortion in the constellation domain (i.e., by moving points off the constellation grid) such that system performance is affected.
Hence, there is still a need for an improved spectrum shaping.